In the past, rubber containing α,β-ethylenically unsaturated nitrile monomer units and conjugated diene monomer units or olefin monomer units (nitrile copolymer rubber) has been known as rubber superior in oil resistance. Its cross-linked products are being used mainly as materials for fuel hoses, gaskets, packing, and oil seals and other various rubber products mainly used around various oils in automobile applications.
In recent years, due to the growing global movement to protect the environment, efforts are being made to reduce the amount of gasoline and other fuels dissipated in the atmosphere, and much lower gasoline permeability is being sought in fuel hoses, seals, packings, and other applications. Further, for fuel hoses, resistance to the free radicals produced in sour gasoline (sour gasoline resistance) is required.
Under these circumstances, Patent Document 1 proposes to stir and mix various types of rubber latexes, montmorillonite suspensions, and montmorillonite dispersants such as pyrophosphoric acid compounds at a high speed to disperse and mix clayey materials in the rubber latexes to improve the properties of the cross-linked products. However, with the method of Patent Document 1, while the obtained cross-linked product was improved in gas barrier property, the gasoline permeability was insufficient.
Further, Patent Document 2 discloses a method of production of a rubber composition preparing a mixture having a rubber-based polymer and a layered inorganic compound and recovering from the prepared mixture a rubber composition containing the rubber-based polymer and layered inorganic compound. However, the object of Patent Document 2 is to obtain rubber cross-linked product superior in vibration damping property and the gasoline permeability and the sour gasoline resistance were insufficient.    Patent Document 1: Japanese Patent Publication (A) No. 2006-70137    Patent Document 2: Japanese Patent Publication (A) No. 2003-201373